This invention generally relates to salt-based formulations having antimicrobial activity and antimicrobial solutions made therefrom. Aspects of the invention have particular utility in connection with water softening and other applications in which ions in a solution may be removed or exchanged.
So-called “hard” water contains excess mineral salts, e.g., calcium and magnesium salts. A variety of techniques have been used to remove or replace ions of these mineral salts to “soften” the water. These techniques include distillation, adding water softening compounds to the water, membrane filtration, and ion exchange, e.g., cation exchange. Ion exchange-based water softening is used in a variety of industrial applications and is particularly prevalent in smaller-scale water softening systems used to treat water coming into individual homes. Ion exchange is also used to remove ions from water and other solutions in other applications.
Generally, ion exchange-based water treatment systems pass water through an ion exchange medium, which exchanges ions in the water with substitute ions, e.g., by exchanging mineral cations with cations of sodium or potassium. A wide variety of such media are known in the art, including resins, which may be strong or weak acid or strong or weak base ion exchange resins, and microporous minerals such as zeolites. For example, U.S. Patent Application Publication No. 2002/0072545 (published Jun. 13, 2002, the entirety of which is incorporated herein by reference), suggests a synthetic ion exchange resin that may comprise a styrene-divinylbenzene copolymer or an acrylic-divinylbenzene copolymer. From time to time, such ion exchange media must be regenerated by exchanging preferred cations for the cations accumulated in the media from treating the hard water. This is typically accomplished by delivering brine to the ion exchange resin during a regeneration cycle that typically lasts on the order of 30 minutes. After passing through the ion exchange medium, the brine is commonly discharged into the environment.
Bacteria may become attached to the surface of the ion exchange medium and proliferate. Over time, the bacteria can create a biofilm on the medium, reducing efficacy of the medium. In some circumstances, the water exiting the ion exchange medium may have a bacteria population that is higher than the bacteria content of the water entering the ion exchange resin. Some opportunistic and disease-causing bacteria that have been found to flourish on ion exchange media may present health risks for the elderly and those with weakened immune systems if present in significant enough concentration. As a consequence, some European countries forbid the use of water softeners without a mechanism for disinfecting the water exiting the water softening system.
Reducing bacterial contamination of ion exchange media by delivering antimicrobial agents to the resin presents a number of difficulties. Calcium hypochlorite is inexpensive and is commonly recognized as a highly effective antimicrobial agent useful in a variety of applications. Unfortunately, calcium hypochlorite is known to reduce the useful life of many common ion exchange resins and manufacturers of such resins caution against its use. A variety of other common antimicrobial agents are ill-suited for applications in which they may be ingested, such as in softening potable water, because of health concerns and/or sensory degradation, e.g., adversely affecting the taste or odor of treated water. Adequately flushing the resin prior to reuse can ameliorate these effects, but consumers may still resist adopting approaches that employ chemicals they deem undesirable. Still other known antimicrobial agents are cost-prohibitive or present environmental waste disposal challenges.